FIG. 1 is a block diagram of a network structure of a universal mobile telecommunications system (UMTS) of a 3GPP asynchronous IMT-2000 system. Referring to FIG. 1, a UMTS mainly includes a user equipment (UE), a UMTS terrestrial radio access network (UTRAN), and a core network (CN).
The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). The RNS includes one radio network controller (RNC) and at least one base station (Node B) managed by the RNC. At least one or more cells exist in one Node B.
FIG. 2 is an architectural diagram of a radio interface protocol between the UE (user equipment) and the UTRAN (UMTS terrestrial radio access network). Referring to FIG. 2, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer. Horizontally, the radio interface protocol includes a user plane for data information transfer and a control plane for signaling transfer.
The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) such as the three lower layers of an open system interconnection (OSI) standard model widely known in the art. The respective layers in FIG. 2 are explained as follows.
A physical layer (PHY) is the first layer and offers an information transfer service to an upper layer using a physical channel. The physical layer (PHY) is connected to a medium access control (MAC) layer located above the physical layer PHY via a transport channel. Data is transferred between the MAC layer and the PHY layer via the transport channel. Moreover, data is transferred between different physical layers, and more particularly, between a physical layer of a transmitting side and a physical layer of a receiving side via the physical channel.
The MAC layer of the second layer offers a service to a radio link control (RLC) layer located above the MAC layer via a logical channel. The RLC layer supports reliable data transfer and is operative in segmentation and concatenation of RLC service data units sent down from an upper layer. Hereinafter, the service data unit will be abbreviated SDU.
A broadcast/multicast control (BMC) layer schedules a cell broadcast message (CB message) delivered from a core network and facilitates broadcasting the message to UEs existing in a specific cell(s). From a UTRAN perspective, the CB message is delivered from a higher layer and is additionally provided with information such as a message ID, a serial number, and a coding scheme, for example. The CB message is delivered to an RLC layer in a BMC message format, and is then delivered to a MAC layer via a logical channel, such as a common traffic channel (CTCH). The logical channel CTCH is mapped to a transport channel, such as a forward access channel (FACH) and a physical channel, such as a secondary common control physical channel (S-CCPCH).
A packet data convergence protocol (PDCP) layer lies above the RLC layer and enables data, which is transferred via a network protocol such as an IPv4 or IPv6, to be efficiently transferred on a radio interface having a relatively small bandwidth. For this, the PDCP layer facilitates reducing unnecessary control information used by a wired network. This function is called header compression, for which a header compression scheme such as RFC2507 or RFC3095 (robust header compression: ROHC), defined by the Internet Engineering Task Force (IETF), can be used. In these schemes, only information mandatory for a header part of data is transferred, thereby reducing data volume to be transferred by transferring a smaller amount of control information.
A radio resource control (RRC) layer is located on a lowest part of the third layer. The RRC layer is defined in the control plane only and is associated with the configuration, reconfiguration and release of radio bearers (RBs) for controlling the logical, transport and physical channels. In this case, the RB is a service offered to the second layer for a data transfer between the UE and the UTRAN. Specifically, the RB is a logical path provided by Layer 1 and Layer 2 of a radio protocol for the data delivery between the UE and the UTRAN The configuration of the RB is a process of regulating characteristics of protocol layers and channels necessary for offering a specific service and a process of setting their specific parameters and operational methods, respectively.
The RRC layer broadcasts system information via a broadcast control channel (BCCH). System information for one cell is broadcast to the UE via a system information block (SIB) format. In case that the system information is changed, the UTRAN transmits BCCH modification information to the UE via a paging channel (PCH) or a forward access channel (FACH) to induce the UE to receive the latest system information.
According to the recent demand for high speed and capacity increment of uplink data in a wireless mobile communication system, a high-speed packet communication system in uplink wherein a user equipment transmits data to a base station is actively discussed. Enhanced uplink dedicated channel (E-DCH) technology is representatively discussed in the 3GPP WCDMA wireless mobile communication system. In the E-DCH technology, uplink packet scheduling by a base station (Node B), HARQ (Hybrid ARQ) in a physical layer and the like are introduced into the conventional 3GPP WCDMA uplink DCH (dedicated channel) to enhance efficiency of uplink.
FIG. 3 is a diagram of a structural example of DCH and E-DCH. Referring to FIG. 3, both DCH and E-DCH are transport channels that can be dedicatedly used by one user equipment (UE). In particular, the E-DCH is used by a user equipment to transfer data to a UTRAN in uplink. Compared to the DCH, the E-DCH can transfer uplink data faster than the DCH. To transfer data at high speed, the E-DCH adopts a technique such as hybrid automatic repeat request (HARQ), adaptive modulation and coding (AMC) and scheduling controlled by a Node B, for example.
For E-DCH, the Node B transfers to the UE downlink control information for controlling the UE's E-DCH transfer. The downlink control information includes response information (ACK/NACK) for HARQ, channel quality information for AMC, E-DCH transport rate assignment information, E-DCH transport start time and transport time interval assignment information, and transport block size information, for example. Meanwhile, the UE transfers uplink control information to the Node B. The uplink control information includes E-DCH rate request information for Node B controlled scheduling, UE buffer status information, and UE power status information, for example. The uplink and downlink control information for E-DCH is transferred via a physical control channel such as an enhanced dedicated physical control channel (E-DPCCH).
A MAC-d flow is defined between a MAC-d sublayer and a MAC-e sublayer for E-DCH. In this case, a dedicated logical channel is mapped to the MAC-d flow. The MAC-d flow is mapped to a transport channel E-DCH, and the E-DCH is mapped to another physical channel E-DPDCH (enhanced dedicated physical data channel). On the other hand, the dedicated logical channel can be directly mapped to DCH. In this case, the transport channel DCH is mapped to a dedicated physical data channel (DPDCH). The MAC-d sublayer in FIG. 3 manages the DCH (dedicated channel) as a dedicated transport channel for a specific user equipment, while the MAC-e sublayer manages the E-DCH (enhanced dedicated channel) as a transport channel used in transferring fast data in uplink.
A MAC-d sublayer of a transmitting side configures a MAC-d protocol data unit (PDU) from a MAC-d service data unit (SDU) delivered from an upper layer, i.e., an RLC layer. A MAC-d sublayer of a receiving side facilitates recovery of the MAC-d SDU from the MAC-d PDU received from a lower layer and delivers the recovered MAC-d SDU to an upper layer. In doing so, the MAC-d exchanges the MAC-d PDU with a MAC-e sublayer via a MAC-d flow or exchanges the MAC-d PDU with a physical layer via the DCH. The MAC-d sublayer of the receiving side recovers the MAC-d PDU using a MAC-d header attached to the MAC-d PDU prior to delivering the recovered MAC-d SDU to an upper layer.
A MAC-e sublayer of a transmitting side configures a MAC-e PDU from a MAC-e SDU corresponding to a MAC-d PDU delivered from an upper layer, i.e., a MAC-d sublayer. The MAC-e sublayer of a receiving side facilitates recovery of the MAC-e SDU from the MAC-e PDU received from a lower layer, i.e., a physical layer and delivers the recovered MAC-e SDU to a higher layer. In doing so, the MAC-e exchanges the MAC-e PDU with the physical layer via the E-DCH. The MAC-e sublayer of the receiving side recovers the MAC-e SDU using a MAC-e header attached to the MAC-e PDU prior to delivering the recovered MAC-e SDU to a higher layer.
FIG. 4 is a diagram of a protocol for E-DCH. Referring to FIG. 4, a MAC-e sublayer supporting E-DCH exists below a MAC-d sublayer of a UTRAN. Furthermore, a MAC-e sublayer supporting E-DCH exists below a MAC-d sublayer of a UE. The MAC-e sublayer of the UTRAN is located at a Node B. The MAC-e sublayer exists in each UE. On the other hand, the MAC-d sublayer of the UTRAN is located at a serving radio network controller (SRNC) in charge of managing a corresponding UE. The MAC-d sublayer exists in each UE.
Control information transmission for E-DCH is explained as follows. First of all, a scheduler exists at a Node B for E-DCH. The scheduler facilitates the allocation of an optimal radio resource to each UE existing within one cell to raise transmission efficiency of data in an uplink transfer at a base station from all UEs within each cell. In particular, more radio resources are allocated to a UE having a good channel status in one cell to enable the corresponding UE to transmit more data. Less radio resources are allocated to a UE having a poor channel status to prevent the corresponding UE from transmitting interference signals over an uplink radio channel.
When allocating radio resources to the corresponding UE, the scheduler does not only consider a radio channel status of a UE. The scheduler also requires control information from UEs. For example, the control information includes a power quantity the UE can use for E-DCH or a quantity of data the UE attempts to transmit. Namely, even if the UE has a better channel status, if there is no spare power the UE can use for E-DCH, or if there is no data the UE will transmit in an uplink direction, a radio resource should not be allocated to the UE. In other words, the scheduler can raise the efficiency of radio resource use within one cell only if a radio resource is allocated to a UE having a spare power for E-DCH and data to be transmitted in the uplink transfer.
Accordingly, a UE should send control information to a scheduler of a Node B. The control information can be transmitted in various ways. For instance, a scheduler of a Node B can instruct a UE to report that data to be transmitted in uplink exceeds a specific value or to periodically send control information to the Node B itself.
In case a radio resource is allocated to a UE from a scheduler of a Node B, the UE configures a MAC-e PDU within the allocated radio resource and then transmits the MAC-e PDU to a base station via E-DCH. In particular, if data to be transmitted exists, a UE sends control information to a Node B to inform the Node B that there is data to be transmitted by the UE. A scheduler of the Node B then sends information indicating that a radio resource allocation will be made to the UE based on the control information been sent by the UE. In this case, the information indicating the radio resource allocation means a maximum value of power the UE can transmit in uplink, a ratio for a reference channel, etc. The UE configures the MAC-e PDU within a permitted range based on the information indicating the radio resource allocation and transmits the configured MAC-e PDU.
In the above description, the Node B can allocate the radio resource to the UE in two ways, via an absolute grant (AG) and a relative grant (RG). The AG indicates an absolute value of a quantity of a radio resource usable by the UE. The RG indicates a variation from a quantity of a radio resource previously used by the UE. Namely, if the UE initially requests a resource allocation, the Node B allocates the radio resource to the UE using the AG. The UE then preferentially sets a serving grant (SG) to a value of the AG and transmits data in uplink within a range of the value. Thereafter, if it is decided that the SG used by the UE is insufficient by considering a channel status, a UE's buffer status, a volume of data to be transmitted and the like, the Node B sends the RG indicating that the UE can raise the SG by a predetermined quantity. If it is decided that the SG used by the UE is excessive, the Node B sends the RG indicating that the UE should lower the SG by a predetermined quantity. The UE then adjusts the SG based on the received RG and always uses the radio resource within a range smaller than the SG.
An E-DCH transport format combination indicator (E-TFCI) indicates information for a MAC-e PDU transmitted via E-DCH. Specifically, the E-TFCI indicates how much data is being delivered. If a transmitting side differs from a receiving side in making a decision regarding information for a transmitted data block, communications cannot be performed correctly. Hence, the transmitting side transmits information necessary for decoding data carried over an enhanced dedicated physical data channel (E-DPDCH), such as a size of the MAC-e PDU, each time the MAC-e PDU is transmitted via the E-DCH. As shown in FIG. 5, the MAC-e PDU is physically transmitted via the physical channel E-DPDCH and the E-TFCI is transmitted via an enhanced dedicated physical control channel (E-DPCCH). In the related art, the MAC-e PDU transmitted via E-DPDCH may contain the data to be transmitted as well as the control information.
The E-DPCCH, which includes information essential to the decoding of the data carried over the E-DPDCH, is much stronger against errors than the E-DPDCH. Thus, a number of bits carried over the E-DPDCH are set to a smaller amount. Currently, a bit number used for the E-TFCI is 7. Accordingly, it can be known that a size of different MAC-e PDUs delivered via the E-DCH is 128 (27=128).
A hybrid automatic repeat request (HARQ) scheme is used for E-DCH to raise a probability of transmitted data successfully arriving at a receiving side and to reduce power necessary for the corresponding arrival. Accordingly, under HARQ, raising the probability of transmission success and reducing necessary power is dependent on feedback information sent from the receiving side to a transmitting side. Preferably, the feedback information notifies whether the data transmitted by the transmitting side correctly arrives at the receiving side.
For instance, if a receiving side correctly receives a packet 1 transmitted by a transmitting side, such as a UE, via a physical channel, the receiving side transmits a reception success signal or acknowledgement (ACK). If the receiving side fails to correctly receive the packet 1, the receiving side transmits a negative acknowledgement (NACK). Thereafter, the transmitting side transmits new data, i.e., a packet 2 in case that the feedback is ACK with reference to the feedback having been transmitted by the transmitting side. If the feedback is NACK, the transmitting side retransmits the packet 1. In doing so, the transmitting side attempts a transmission using both of the former packet 1 (firstly transmitted) and the latter packet 1 (secondly transmitted). If this succeeds, the receiving side transmits ACK to the transmitting side. If this fails, the receiving side transmits NACK to the transmitting side. When NACK is received by the transmitting side, the transmitting side repeats the above process. In this case, the retransmitted packet 1 should be identical to the former packet 1. If not, the receiving side is unable to recover the data correctly.
However, if the UE continues to stay in an area having a poor channel status or if data to be transmitted by the UE is sensitive to delivery delay, the UE is unable to indefinitely perform the above-explained retransmission. Therefore, the receiving side informs a UE of a maximum number of available transmissions or retransmissions. In case of receiving the NACK from the receiving side after having attempted to transmit data as many times as the maximum number of retransmissions, the UE stops attempting the transmission of the corresponding data and attempts a transmission of next data.
In the related art, a UE includes control information, such as its buffer capacity, a quantity of power usable for E-DCH and the like in a MAC-e PDU and transmits the MAC-e PDU; however, the HARQ transmission scheme is used for transmitting the MAC-e PDU. Namely, the MAC-e PDU is hardly delivered by a single transmission. Instead, several retransmissions are needed until a receiving side correctly receives the MAC-e PDU. Thus, a delivery delay corresponding to each retransmission occurs. Accordingly, since information such as a power quantity and a buffer capacity usable by a UE in uplink is frequently changed, the occurrence of the delivery delay degrades a quality of service felt by a user.
When a user uses a service such as a web page search, a quantity of data transmitted in uplink is very small. In most cases, uplink data will include only one packet. Nonetheless, in accordance with the related art method, a UE includes control information for indicating the presence of data to be transmitted in uplink in a MAC-e PDU and transmits the MAC-e PDU. A Node B then transmits information indicating a radio resource allocation. Afterward, the UE transmits the corresponding data in uplink.
However, the related art method has the following problems. First, it takes a considerable amount of time to exchange control information between the UE and the Node B. Second, in using a MAC-e PDU to send control information, the MAC-e PDU is transmitted via E-DPDCH. As mentioned in the foregoing description, E-TFCI should be used to transmit the MAC-e PDU comprising the control information via E-DPCCH because of the strength of E-DPCCH against errors. Namely, both the E-DPDCH and the E-DPCCH are used for the transmission of one control information, whereby power is considerably wasted.